By the F-T synthesis method developed by Fischer and Tropsch, who are German chemists in 1923, it is possible to produce liquid hydrocarbon from coal, natural gas, biomass, and the like through synthesis gas. A process of producing liquid hydrocarbon from coal is referred to as a coal-to-liquids (CTL) process, a process of producing liquid hydrocarbon from natural gas is referred to as a gas-to-liquids (GTL) process, and a process of producing liquid hydrocarbon from biomass is referred to as a biomass-to-liquids (BTL) process, and similar processes are collectively referred to as an XTL process recently. The processes first change each source material (coal, natural gas, biomass, and the like) to synthesis gas by using a gasification method, a reforming method, and the like. For a composition of synthesis gas appropriate to the XTL process for producing liquid fuels, a ratio of hydrogen to carbon monoxide may be approximately 2 as represented in an equation below.CO+2H2+—[CH2]—n→—[CH2]—n+1+H2O
CO, H2, —[CH2]—n, H2O represent carbon monoxide, hydrogen, hydrocarbon having a chain length of n (n carbon atoms), and water, respectively. However, when a ratio of hydrogen is high, selectivity of methane is increased, so that selectivity of C5+ (hydrocarbon with 5 carbon atoms or more) is relatively decreased, the high ratio of the hydrogen is not appropriate. Olefin, oxygenate (molecule containing atomic oxygen, such as alcohol, aldehyde, and ketone), and the like, as well as hydrocarbon having a linear chain with the aforementioned form, are generated as a by-product.
Since one of the main purposes of the XTL process is to obtain liquid fuel, it is a recent trend to produce linear hydrocarbon, especially, linear hydrocarbon with C5+, with high selectivity by optimizing a cobalt-based catalyst, a ratio, temperature, pressure of synthesis gas, and the like. An iron-based catalyst is the most widely used catalyst, other than the cobalt-based catalyst. The iron-based catalyst is mainly used in the early days, and is cheaper than the cobalt-based catalyst, has low methane selectivity at a high temperature, and has high olefin selectivity among hydrocarbon, and many products based on olefin, other than liquid fuels, are generated. Compared to this, the cobalt catalyst mainly generates liquid fuels, generates less carbon dioxide, and has a long life span. However, the cobalt catalyst is very high in price than iron, methane selectivity thereof is increased, so that the cobalt catalyst needs to be reacted at a low temperature, and the cobalt catalyst is high in price, so that it is necessary to use the cobalt catalyst by distributing well a small amount of cobalt catalyst on a surface of a support. Refractory oxide materials such as alumina, silica, titania, and the like are used as the support, and performance thereof is improved by using noble metal, such as Ru, pt, and Re, as a cocatalyst.
A form of the reactor considered up to now is classified into a tubular fixed bed reactor, a fluidized bed reactor, and slurry phase reactor, and the representative fluidized bed reactors are a circulating fluidized bed reactor and a fixed fluidized bed reactor. Since a reaction characteristic and distribution of a product are influenced according to the form of the reactor, the form of the reactor needs to be appropriately selected considering a target final product.
As far as commercialization is concerned, the fluidized bed reactor among the reactors is mainly operated at a high temperature, and a main component of the final product is gasoline, and light olefin. The tubular fixed bed reactor and the slurry phase reactor are mainly appropriate for producing diesel, lube base oil, wax, and the like, and are commercially operated by a low-temperature F-T process. In the low-temperature F-T process, hydrocarbon of 60% or more having a higher boiling point than that of diesel is generated, so that diesel is additionally produced through a subsequent process, such as hydrocracking, and a wax component is changed to high-quality lube base oil through a dewaxing process to be used. In comparison between the fixed bed reactor and the slurry phase reactor representative in the low-temperature F-T reaction, the slurry phase reactor has advantages as follows.                An apparatus expense and a construction expense are low.        Heat and material transfer efficiencies are high.        Axis-directional pressure drop is small.        Productivity (productivity per volume of the reactor) is high.        It is easy to charge catalyst particles, and it is possible to additionally charge and discharge the catalyst during an operation.        
In respect to the aforementioned advantages, the slurry phase reactor has been preferred, but the product is mixed with catalyst particles to be obtained as a slurry phase, so that a method of effectively separating the liquid hydrocarbon from the catalyst particles is demanded. In this respect, a filtration method, a centrifugation method, a magnetic separation method, a separation method using hydrocyclone are widely known as a representative method.
Reviewing the filtration method, a filtration apparatus may be divided into an internal filtration apparatus and an external filtration apparatus according to an installation position of the filtration apparatus. U.S. Pat. Nos. 6,462,098 and 7,098,251 disclose an example in which a filtration apparatus is installed inside a slurry phase reactor, and U.S. Pat. No. 7,008,966 represents a conceived example in which a filtration apparatus installed inside may be removed, and U.S. Pat. No. 6,929,754 discloses an example in which filtering performance is improved by installing a filtration apparatus outside a reactor and adjusting a filter cake. Further, a magnetic separation method, which needs high-priced equipment but has excellent separation performance for an iron catalyst, has been attempted (Energy & Fuels, Vol. 10, No. 5, 1996). U.S. Pat. Nos. 4,919,792 and 6,974,842 describe that a centrifugal separator may be applied to separation of a catalyst from slurry, and above this, various catalyst separation methods have been reported in many patents and documents.
As described above, various catalyst particle separation methods have been disclosed, but there is a limit in that the catalyst is separated only by the filtration method because fine catalyst particles or fragmented catalyst particles during a slurry reaction block fine filter holes. Further, there is a disadvantage in that the centrifugal separator has a burden in operating a rotation device, and a sedimentation method takes a long time. The magnetic separation method is an effective method, but is very high in price and an applicable catalyst is limited to a few kinds of catalysts.
One of the most important issues which should not be overlooked in the catalyst particle separation method is a catalyst agglomeration phenomenon. The catalyst agglomeration phenomenon refers to a phenomenon in which fine catalyst particles or small fragmented particles during the reaction are tangled with each other together with liquid hydrocarbon, co-produced water, and the like to be agglomerated.
Various attempts and researches have been reported due to the catalyst agglomeration phenomenon, and according to Korean Patent Application Publication No. 2010-0034970, it is described that the agglomeration phenomenon may be considerably solved by adding alcohol having a high boiling point, which is greatly helpful to improve long-time operation stability of the catalyst and extend a life span of the catalyst. Further, according to the U.S. Pat. No. 5,977,192, a problem was found in that a agglomeration phenomenon is generated due to a contact with liquid hydrocarbon when fine catalyst particles with less than 20 μm are injected to the reactor so that the catalyst particles are not distributed well inside the reactor, and process performance was improved by adding alcohol, ketone, ester, ether, or a mixture thereof, which is liquid polar oxygenate, not acidic.
A method of suppressing agglomeration by adding an additional additive like the aforementioned methods is highly preventive to be helpful for a fundamental solution, but the fact is obvious that the catalyst is fragmented due to accumulation of catalyst fatigue caused by a long-time operation or it is impossible to completely prevent fine catalyst particles, which are inevitably inserted at a predetermined portion when an additional catalyst is injected, from being aggregated. In addition, it is necessary to consider increase in an expense and other additional problems generated by injecting an additional compound during the process, and the large amount of expense is caused by separating and refining a tiny amount of compound even though the alcohol with the high boiling point or the polar oxygenate is replaced with similar kinds of by-products co-produced during a producing process.
Accordingly, a new reactor and separation method capable of removing agglomerated or aggregated catalyst lumps is demanded.